So far, the second-generation (2G) system and the third-generation (3G) system have been mainly used, and in recent years, standardization of Long Term Evolution (LTE), which is the fourth-generation (4G) system, is under way.
Since the LTE system basically supports only the packet services, the LTE standard has proposed a so-called Circuit Switched FallBack (CSFB) service to provide voice services to users of the LTE system.
FIG. 1 schematically illustrates a configuration of a wireless communication system supporting a CSFB function.
Referring to FIG. 1, an LTE system 110 includes an Evolved Packet Core (EPC) 111 and an evolved Node B (eNB) 113. Although not illustrated, the EPC 111 includes a Mobility Management Entity (MME) responsible for a control plane, and a Serving GateWay (S-GW) and a PDN GateWay (P-GW) responsible for a user plane. A 2G/3G legacy system 130 includes a Mobile Switching Center (MSC) 131 responsible for call switching processing, and a Base Station (BS) 133.
The CSFB service refers to a service, in which if a voice call occurs to a User Equipment (UE) 150 which is capping on the LTE system 110, the UE 150 is handed over to the existing 2G/3G legacy system 130 to connect the voice call.
During the CSFB process, the UE 150 is handed over from the LTE system 110 to the 2G/3G legacy system 130. At this point, in order to select an appropriate cell (for example, a cell with a good channel status) from among the undepicted 2G/3G cells around the UE 150 and switch the UE 150 to the selected cell, the LTE system 110 may receive measurement reports on the 2G/3G cells from the UE 150.
However, compared to when setting up a voice call directly in the existing 2G/3G legacy system, if it uses CSFB, the UE 150 additionally needs the time required for switching from the LTE system to the 2G/3G legacy system and measuring the cell status, causing delays that degrade the Quality of Service (QoS) in the CSFB service.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.